Refrigerator defrosting apparatus



Jan. 18, 1966 E. L. WILSON ETAL 3,229,474

REFRIGERATOR DEFROSTING APPARATUS Filed March 14, 1963 2 Sheets-Sheet 1INVENTOR. EUGENE L. WILSON BENJAMIN M. SMITH J n- 1966 E. L. WILSON ETAL3,229,474

REFRIGERATOR DEFROSTING APPARATUS Filed March 14, 1963 2 Sheets-Sheet 2s7 ZI E- I II L] CUE LJQ Li -2 INVENTOR EUGENE L. WlLSON BENJAMIN M.SMITH 3,229,474 Patented Jan. 18, 1966 fitice 3,229,474 REFRIGERATORDEFROSTING APPARATUS Eugene L. Wilson, 3207 Kentucky Ave., Baltimore 13,Md., and Benjamin M. Smith, 4994 Denmore Ave., Baltimore 15, Md.

Filed Mar. 14, 1963, Ser. No. 265,196 2 Claims. (Cl. 62-140) Thisinvention relates generally to defrosting apparatus and morespecifically to an electrical defroster which is independent of anytiming action and assures a positive determination for the defrostcycle.

Many types of defrosting systems for both commercial and domesticrefrigerator use are known today. Generally, these types of defrosterseither use a separate heat source such as an electrical resistanceheater or a reverse refrigeration cycle wherein the warmer refrigerantis pumped through the coils in order to defrost the evaporator. Most ofthe defrosters have a timer which controls the start and termination ofa defrost cycle. Not only do these timers add to the expense ofmanufacturing the defrosting apparatus but they also provide a setdefrosting cycle which oftentimes provides defrosting when it is notreally necessary or, conversely, which terminates the defrost cyclebefore the coils become completely defrosted.

Attempts have been made to overcome this type of operation by providinga defrosting apparatus which is initiated by a build up of the frost onthe coils, thus providing a defrost cycle only when it is necessary.However, once the defrosting cycle is started, a timer is still used toterminate the defrost period and thus there is no termination pointrelated to the amount of frost on the coils. This also can result ineither too short a cycle or one that extends beyond the time necessary,resulting in possible damage to the equipment and the coils.

It has been proposed that this defect could be overcome by using coilswhich are movable and which are supported by some resilient meanswhereby a defrost cycle will be started as a result of the weight of theice building up to a predetermined amount on the coils thus causing thecoils to drop and cut on a switch to an electrical heater. In this typeof operation the cycle is terminated when enough of the frost has meltedto reduce the weight on the coils and allow them to gradually return totheir original position. To the best of our knowledge, this type ofdefrosting apparatus has never proved to be satisfactory, primarily dueto the fact that there are too many variables which add to or subtractfrom the weight of the coils besides the frost alone. These include thevarying weight of the refrigerant itself and the oil which is naturallyin the system. Although this does not materially affect the start of thecycle under this proposed type of system, it does vary enough to holdthe coils in the defrost position even when the coils are completelyfree from any ice.

Accordingly, it is an object of this invention to provide defrostapparatus for a refrigerating system which is entirely independent ofany timing device.

Another object of this invention is to provide defrost apparatus whicheliminates unnecessary defrost cycles.

Yet another object of this invention is to provide defrosting apparatuswhich has a positive termination point independent of the weight of thecoils and the gas therein.

A further object of this invention is to provide a simplified defrostingcycle wherein the cycle is terminated by means of gas pressure whichvaries proportionately with the heat supplied during the defrost cycle.

These and other objects will become apparent from the followingdescription when taken in conjunction with the drawings wherein:

FIG. 1 is a diagrammatic showing of one form of the present invention;

FIG. 2 is a schematic of the electrical circuitry used in connectionwith FIG. 1; and

FIG. 3 is a partial schematic of a modified version of the apparatus ofFIG. 1.

Generally speaking, the invention comprises an automatic defrostingmeans used in conjunction with refrigerating systems includingevaporator coils which comprises a means for pivotally mounting thecoils at one end thereof within an enclosure, resilient means within theenclosure for supporting the other end of the coils, means within theenclosure for releasably retaining the coils in first and secondpositions about the pivotal mounting means, a resistant heater withinthe enclosure, a switch actuated by the releasable retaining means forsupplying electric power to the heater when the coils are in theirsecond position, pneumatic pressure means within the enclosure adaptedto contact and move the coils from the second to the first position inresponse to a predetermined pressure applied thereto, and tubing coupledto the pneumatic pressure means and containing refrigerant gas which isresponsive to the heat created by said resistance heater, the heatincreasing the pressure of the gas within the tubing thereby actuatingthe pneumatic pressure means.

Turning now more specifically to the drawings, there is shown in FIG. 1an evaporator coil 11 having a closed circuit configuration through thecondenser and compressor 21 which is driven by a motor 23 throughmechanical coupling 25. Also shown are the normal dissipating plates 13directly connected to the evaporator coil 11. The coil 11 is supportedin a movable manner by means such as a U-shaped supporting structure 15which is mounted pivotally at 19 to the base 17 of the enclosure. Forpurposes of clarity the remaining part of the enclosure is not shown.

In the specific illustration of FIG. 1, an arm 27 extends from thesupport structure 15 and moves substantially vertically as the supportmember rotates about pivot 19. In order to provide a support for theouter end of the structure 15, a compression spring 29 is located belowthe arm 27. Spring 29 rests on base cup 33 which is mounted on the baseportion 35 of the enclosure. Secured to the top of the spring is a cup31 which bears against the adjustable screw 37. By providing theadjustable screw, the position of the coils in their dry or defrostedcondition may be set with relation to spring 29. Since the positioningof the coils higher above plate 31, by means of screw 37, would requirea greater compression of spring 29 before actuation of switch 51, alarger total coil and frost weight would be needed for such actuation.Accordingly, such adjustment provides a means whereby the start of thedefrost cycle can be adjusted in accordance with varying amounts offrost accumulation on the coils 11 and plates 13. Thus, the same resultis achieved as would be if the tension of spring 29 were adjustable andthe plate 31 were to bear directly against arm 27.

A bellows 39 is also mounted below arm 27 on the base 35. This bellowsmay be made of a material such as copper which will not be attacked bynormal refrigerant gases in use today. A capillary tube 41 connects theinner chamber of the bellows to the low side of the evaporator coil at43 for purposes which will be more thoroughly discussed as thedescription proceeds. It will be evident that, as the bellows expands,the plate 45 secured to the top thereof will abut against the adjustablescrew 47, thus providing an upward force against the arm 27 resulting ina return of the coils to the refrigerating position.

A lever 49 is secured to the outer end of arm 27 by means such aswelding and, as indicated schematically in FIG. 2, is connected to a twoposition snap action switch 51 employing springs 63 and 65. Therefore,the lever can only be in one of two positions, the first of which is asshown in FIG. 1 when the refrigerating process is normally underway andthe second position being that of a lowered position which initiates thedefrost cycle.

A switch 51 is actuated by the lever 49 and controls the basicrefrigerating and defrost power supply. Switch 51 is connected by meansof leads 53 and 54 to the motor 23 and resistance heater 59.

The operation of the device will be explained in connection with theelectrical schematic of FIG. 2 and the apparatus of FIG. 1. With thedevice in the position shown in FIG. 1, the normal refrigeratingcondition exists with the compressor-condenser 21 delivering therefrigerant to the evaporator coils in the usual manner. When the frostis accumulated on the coils to a sufificient extent, the additionalweight overcomes the tension of the compression spring 29 and the coilscommence to drop in a counter clockwise direction about pivot 19. Whenthe coils have dropped far enough to force the lever 49 past itsmidpoint position the snap action of the springs will force the leverdown into its second position, thereby holding the coils against theforce of the compression spring 29. 4

Under the refrigerating cycle the bellows are designed so that they arein their nonexpanded condition since the gas in the lower side of theevaporator coils and in the capillary tubing 41 is at a low temperatureand pressure.

When the coils are in their lowered position, the snap action lever 49moves the double pole switch 51 to the position illustrated in FIG. 2.In this position, the circuit from the power source 67 to the motor 23has been broken by removing the switch blade from the contact 56. Thisstops the operation of the motor 23 and terminates the operation of thecompressor-condenser 21. At the same time the switch blade makes contactwith terminal 58, completing the circuit to the heater 11 by means oflead 53 through the fail safe thermostat 57. The thermostat 57 may be ofany of the well known types, and has no effect on the operation of thedevice with the exception that if the coils should get bound in theirdown or defrost position, the excess amount of heat generated by theelectrical heater 59 would cause the bimetallic arm 60 of the thermostatto contact terminal 62, removing the power supply from heater 59 andclosing the circuit to the motor through alternate lead 55, thusresuming the refrigeration operation.

As the heater 59 begins operation the frost on the coils starts to melt,and when the point is reached wherein all the frost has been eliminatedfrom the coils the temperature of the gas within the evaporator coil 11will begin to rise. As the temperature of the gas rises the pressurewithin the coil will also rise due to the fact that the increasedtemperature causes the refrigerant gas to expand. This also causes thepressure in the capillary tubing 41 to increase, which raises thepressure in the interior chamber of the bellows 39 causing it to expand.Depending upon the position of screw 47, the bellows will contact thescrew at a predetermined pressure forcing the coil arm 27 upwardly whichrotates the coils clockwise about pivot 19. When the arm 27 has beenraised to a point just beyond the center point of the snap action lever49 the springs will cause the arm 27 to snap back into its firstposition. This operation provides a positive termination of the defrostcycle since the arm 27 moves the switch 51 from contact with terminal 58which opens 4 the circuit to the heater, and contacts terminal 56 whichcloses the circuit to the motor.

As will now be evident, this invention provides a device wherein thedefrost cycle is started only when necessary and terminated, not by anytimer nor by a decrease of weight about the coils, but by a positivedetermination that the coils themselves are free of any frostthroughout.

FIG. 3 shows a modification of the above discussed invention whereinrefrigerant gas is contained within a thermal bulb 71 which is locatedadjacent the plates surrounding the evaporator coil. Again, the heatwill react on the gas within the thermal bulb, raising its temperatureand pressure which increases the pressure within the capillary tube 69causing the bellows to expand. While the embodiment of FIG. 3 has beenfound to operate satisfactorily, it does not absolutely assure acomplete defrost of the entire coil since the bulb 71 must be locatedsomewhere along the length of the coil. However, the basic principle ofthe invention is still provided since termination of the defrost cycleis controlled by a gas expansion governed by the heat generated in theevaporator coils and plates. In both embodiments the capillary tubinghas enough flexibility to allow for the relatively small movement of thecoils.

It is to be understood that the present invention has been described andshown in one particular illustrative manner but is not to be consideredlimited thereto. The location of the various support members, heatersand pneumatic device could be varied without departing from theinvention. Additionally, other means for placing the coils in either oftwo positions could be used in place of the snap action lever. Oneexample would be the use of dual magnets to which the lever would beattracted, therefore preventing the lever from attaining a positionbetween the refrigerating and defrost cycles.

Accordingly, the invention is limited only by the scope of the followingclaims.

We claim:

1. In refrigerating apparatus,

an evaporator cooling coil pivotally mounted at one end thereof,

resilient means for supporting the other end of said coil,

means for releasably retaining the other end of said coil in first andsecond positions about said pivotal mount,

means for heating said coil,

switch means actuated by said coil when in said second position forinitiating operation of said heating means,

a bellows means responsive to the pressure in said cooling coil forcontacting and moving said coil from said second to said first positionat a predetermined pressure thereby disconnecting said heating means,and

means for varying the point at which the bellows moves said coil inorder to adjust the return of said coil to said first position.

2. In a refrigerating system including evaporator cooling coils mountedwithin an enclosure, automatic defrosting means comprising,

means for pivotally mounting said coils at one end thereof within saidenclosure,

resilient means within said enclosure for supporting the other end ofsaid coils,

means within said enclosure for releasably retaining said coils in firstand second positions about said pivotal mounting means,

a resistance heater within said enclosure,

a switch actuated by said releasably retaining means for supplyingelectric power to said heater when said coils are in said secondposition,

pneumatic p essure means within said enclosure adapted to move saidcoils from said second to said first position in response to apredetermined pres sure applied thereto,

tubing means coupled to said penumatic pressure means and containing arefrigerant gas responsive to the heat created by said resistanceheater, said heat increasing the pressure of said gas Within said tubingmeans thereby actuating said pneumatic pressure means, and

means for adjusting the point at which said pneumatic pressure meansmoves said coils.

References Cited by the Examiner UNITED STATES PATENTS Dick 62-156 XKagi 62-140 Hull 62209 X Heitman 62-140 Smith 62140 Johnson 62140 10ROBERT A. OLEARY, Primary Examiner.

1. IN REGRIGERATING APPRATUS, AN EVAPORATOR COOLING COIL PIVOTALLYMOUNTED AT ONE END THEREOF, RESILIENT MEANS FOR SUPPORTING THE OTHER ENDOF SAID COIL, MEANS FOR RELEASABLY RETAINING THE OTHER END OF SAID COILIN FIRST AND SECOND POSITIONS ABOUT SAID PIVOTAL MOUNT, MEANS FORHEATING SAID COIL, SWITCHING MEANS ACTUATED BY SAID COIL WHEN IN SAIDSECOND POSITION FOR INITATING OPERATION OF SAID HEATING MEANS, A BELLOWSMEANS RESPONSIVE TO THE PRESSURE IN SAID COOLING COIL FOR CONTACTING ANDMOVING AND MOVING SAID COIL FROM SAID SECOND TO SAID FIRST POSITION AT APREDETERMINED PRESSURE THEREBY DISCONNECTING SAID HEATING MEANS, ANDMEANS FOR VARYING THE POINT AT WHICH THE BELLOWS MOVES SAID COIL INORDER TO ADJUST THE RETURN OF SAID COIL TO SAID FIRST POSITION.